System and method for reproducing colors on a printing device

ABSTRACT

A method and a system for outputting an image having a specific color on an output device, the method including (a) analyzing the image; (b) creating a model for the output device, based on the analysis, wherein the model encompasses the specific color and is made in a particular space having a one-to-one relation to a device independent color space.

This application is a national stage filing under 35 USC §371 of PCTapplication No. PCT/EP2003/050298 filed Jul. 9, 2003 which claimspriority to EP application no. 02102020.1 filed Jul. 10, 2002 and U.S.provisional patent application No. 60/406,450 filed Aug 28, 2002.

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for thereproduction of color documents; the invention especially concerns colormanagement. The invention is particularly suitable for the reproductionof objects defined by a mixture of process inks and non-process inks.

BACKGROUND OF THE INVENTION

Today, more and more output systems are developed for the reproductionof color images. Several display and printing technologies are used suchas CRT's, LCD's, conventional photography, electrophotography, thermaltransfer, dye sublimation and ink jet systems to name a few. In the restof this document, these systems will be referred to as output devices.

All these systems can be described as multi-dimensional color deviceswith n colorants such as CMYK (cyan, magenta, yellow and black) inks ofan ink jet system or RGB (Red, Green, Blue) in case of a display system.In this document it is assumed that the colorant values for printersrange from 0% (no colorant laid down on paper) to 100% (maximum amountof colorant laid down on paper). For display systems, the values rangefrom 0 to 255. In the rest of this document, mainly a printer will beused as an example of an output system, however, it is well known in theart of color management systems that all aspects of printers can beeasily extended to those of display systems.

With colorant space is meant an n-dimensional space, wherein n is thenumber of independent variables with which the output device can beaddressed. For an offset printing press e.g., the dimension of thecolorant space equals the number of inks of the printing press. If CMYKinks are used, the dimension of the colorant space is four. Colorantspaces are also referred to as device dependent spaces.

The colorant gamut is defined by all possible combinations of colorantvalues, ranging from 0% to 100% for printers and from 0 to 255 fordisplay systems, taking into account a number of specified colorantlimitations. If there are no colorant limitations, the colorant gamut isan n-dimensional cube.

With calorimetric space is meant a space that represents a number ofquantities of an object that characterize its color. In most practicalsituations, colors will be represented in a 3-dimensional space such asthe CIE XYZ space. However, also other characteristics can be used suchas multi-spectral values based on filters that are not necessarily basedon a linear transformation of the color matching functions. The valuesrepresented in a calorimetric space are referred to as calorimetricvalues. Colorimetric spaces are also referred to as device independentspaces or as color spaces.

A printer model is a mathematical relation that expresses calorimetricvalues in function of colorants for a given output system. The variablesfor the colorants are denoted as c₁, c₂, . . . , c_(n) with n thedimension of the colorant space. An n-ink process is completelycharacterized by its colorant gamut with a number of colorantlimitations and the printer model. Because of this close relationshipbetween an n-ink process and the printer model, the operations typicallydefined for a printer model are easily extended to an n-ink process.

The printer model is often based on a printer target. Such a targetconsists of a number of uniform color patches, defined in the colorantspace of the printing device. In a next step the printer target isprinted and measured, and based on the values of the patches in colorantspace and the measured colorimetric values, the printer model is made. Aprinter target is normally characterized by a number of sampling pointsalong the different colorant axes. Based on the sampling points aregular grid can be constructed in colorant space of which a number ofgrid points are contained by the printer target. Hence a target can besaid to be complete or incomplete. We refer to patent application EP-A-1146 726, herein incorporated by reference in its entirety for backgroundinformation only, for more information on grids, complete and incompleteprinter targets, and related terms.

With inverting an n-ink process is meant that the corresponding printermodel is inverted. The transformation of an n-ink process tocolorimetric space on the other hand is equivalent to the transformationof the corresponding colorant gamut to color space by making use of theprinter model.

We refer to patent application EP-A-1 083 739, herein incorporated byreference in its entirety for background information only, for moreinformation on colorant spaces, color spaces, and other relevant terms.

Based on a printer model, forward and inverse look up tables areconstructed. These tables are also referred to as tables or colortables. A forward table transforms colorant values to calorimetricvalues whereas the inverse tables transforms calorimetric values tocolorant values. Inverse tables are also called separation tables orcolor separation tables.

The present invention is related to the rendering of page descriptions,consisting of multiple page elements such as text, different types ofimages and color gradations (color gradations, also called colorvignettes, are elements wherein color smoothly changes from one color toanother one).

In most cases, the page elements are described in a calorimetric orcolorant space, which may either be a device independent color spacesuch as CIELAB, or a device dependent space such as RGB or CMYK. If thepage has to be reproduced on a given output system, such as a printer ora display system, the color values have to be transformed to the propercolorant values of the concerned output system. This transformation isrequired as the color space of the page elements is in most casesdifferent from the color space of the output system. In fact for mostdocuments it is not known in advance on which output system the documentwill be reproduced and the different page elements may be defined indifferent color spaces. Hence to reproduce these page elements, eachelement is preferably color managed by making use of proper colortransformations.

In a lot of cases, all page elements are defined in the sameconventional color space. Depending on the application, this is usuallya device dependent RGB, CMY or CMYK space. In home office environments,the RGB space corresponds to a monitor space and preferably the sRGBspace is used. In a graphic arts environment, the CMYK values aretypically standard Euro, SWOP or standard newspaper colorant values.

If the output system is known on which the document has to bereproduced, the color values have to be transformed unless the colorspace of the page elements corresponds to the color space of the outputdevice. Such a transformation is in most cases done with color tables. Aworldwide-accepted system to transform the colors is given by the ICC,the International Color Consortium. With this approach, each device ischaracterized to or from a device dependent color space. Such atransformation is described by tables, matrices and TRC's (ToneReproduction Curves, i.e. one-dimensional look up tables) which arestored in a profile. In most cases profiles contain both forward andinverse color tables. Hence, if all page elements have the same colorspace, profiles can be used to perform the proper color managementoperations.

If on the other hand different page elements are defined by differentbut conventional color spaces, and these spaces can be describedproperly by conventional profiles, then the ICC approach can also beapplied easily. To support this functionality, different applicationsallow the embedding of profiles in images.

For a number of page elements, however, ICC profiles do not yield goodresults. This is the case when non-process colors or a combination ofprocess and non-process colors are used. Process colors are thecolorants used in conventional printing processes such as CMYK fornormal offset printing, or cyan, magenta, yellow, black, orange andgreen in case of Hexachrome™ printing. In addition to process colors,non-process colors may be used, such as custom colors and spot colors. Acustom color is a colorant especially created for a particularapplication. Spot colors on the other hand are colorants that aretypically used if images are created artificially. The designer of theimage then chooses one or more spot colors to render some image portionsmore accurately. In practice, a spot color is chosen out of a setcontaining tenths or hundreds of colorants. Spot colors are also callednamed colors.

Since a spot color is chosen out of a very large set of colorants, it isnot practical to make color tables to describe the mixing of one orseveral spot colors.

As only the calorimetric values of the 100% patch are known, a spotcolor is usually rendered by transforming the calorimetric values of the100% patch to the colorant values of the output device. By making use ofsimple interpolation techniques, colorant values for in between dotpercentages of the spot color can be obtained.

More complicated is the situation in which multiple spot colors, or spotcolors and process colors are printed on top of each other. Due to thevery large number of possible color combinations, it is practicallyimpossible to print the most elementary combinations in order to be ableto construct an accurate printer model.

Therefore, if spot colors are printed on top of each other, it iscustomary to calculate the overlap simply by adding the colorant valuesof the individual spot colors. Take for example an overlap of 40% of afirst spot color and 70% of a second spot color, and suppose that thecolorant space of the output device is CMYK. The CMYK colorant values ofthe 40% patch are determined from values of the 100% patch of the firstspot color, and those of the 70% patch are determined from the 100%patch of the second spot color. The color of the overlap is thenpredicted by adding the CMYK values of the 40% and those of the 70%patch. However, this solution is not accurate.

There is thus a need for an improved method.

SUMMARY OF THE INVENTION

The present invention is a method for outputting an image having aspecific color on an output device, the method including the steps of:analyzing the image for an overlap of the specific color with anothercolor; creating a model for the output device, based on the analysis,wherein the model encompasses the specific color, uses spectralinformation of the specific color and is created in a particular spacehaving a one-to-one relation to a device independent color space.Preferably a method in accordance with the invention is implemented bycode run on a computer.

An embodiment of the present invention is explained by reference to thedrawing. A dedicated printer model is created 104 describing the colormixing of a non-process color with a given number of non-process colorsand/or process colors. To build the model 104, the colorant combinationsof the image need to be known. In a preferred embodiment of theinvention, the image 100 is therefore analyzed 102, and the model iscreated, based on the analysis. One or more image characteristics may beextracted from the image and used in creating the model.

As mentioned above, customarily a printer model 101 is created beforethe image is processed. Usually the printer model is based on a printertarget that is printed by means of the process colors, which are oftenCMYK. The printer model is then used in reproducing portions 103 ofimages that are composed of process colors. As mentioned above, forimage portions wherein non-process colors are used, a second, verysimple approach is used wherein the non-process colors are converted toCMYK and, in case of overlapping non-process colors, the CMYK values ofthese non-process colors are added.

In a method in accordance with the invention, the second model ispreferably created 104 in another space than CMYK space. Advantageously,the model is created in a device independent space, such as CIELAB or,which is preferred, CIE XYZ. A space that has a one-to-one relation to adevice independent space, such as sRGB, may also be used. Moreover, itis preferred to use another model than the simple addition of colorantvalues, in case of overlapping colors spot colors. In one embodiment ofthe invention, the spectral Neugebauer equations are used, as isdiscussed further below. Such a model in accordance with the inventionis completely different from the customary simple addition in CMYKspace. Preferably, to create the model, information is used on whatnon-process colors are present in the image. More preferably, alsoinformation is used on the occurrence of overlaps of non-process colorswith each other and with process colors. Such information is included inthe data of the image that is to be output, and can be extracted fromthe image by analyzing the image data.

The dedicated printer model is used to transform 105 the portions of theimage that include non-process colors. On these transformed portions,the inverse printer model 106 is applied for transforming these portionsinto the process colors so that they can be reproduced 107 on theprinter.

An advantage of the invention is that spot colors, and especially theoverlap of spot colors with each other or with other colors, arereproduced with higher color quality.

Another advantage is better reproduction of the transition betweenprocess colors and non-process colors.

A preferred application is proofing an image on a proofing device, alsocalled proofer, before it will be printed on another output device suchas an offset press. The proofer is preferably an ink jet printer.

BRIEF DESCRIPTION OF THE DRAWINGS

The Drawing is a flowchart of a process of a preferred embodiment of thepresent invention.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

If in a page description an object is defined by a non-process ink, atechnique is required to reproduce the object in a way that is inagreement with the expectations of the customer. In the graphic arts,such a non-process ink is called a spot color; such an ink is used inthe design of an image to create special color effects.

If the images designed for an offset system need to be simulated on aproofer or reproduced on another output system, profiles can be used totransfer the offset color values to a device independent color spacewhereas the profile corresponding to the output system will transferthese color values further on to the colorant values of the outputsystem. This method is used for the process colors (which are usuallyCMYK). As mentioned before, no color tables are available for spotcolors and hence, the color values corresponding to colorant values ofspot colors have to be predicted in another way.

In graphic arts, a phenomenon that influences the reproduction of colorsis dot gain. To reproduce an image by means of offset printing, colorseparations are made for the printing plates. If only process colors areused, typically separations corresponding to the cyan, magenta, yellowand black ink are generated, resulting in four printing plates. However,if also additional spot colors are to be printed, for every spot coloran additional separation has to be made, resulting in an additionalprinting plate. Each printing plate is used to print one of the inks ona receiving substrate, such as paper. In printing, the dot size on paperappears to be larger than the dot sizes sent to the printing system.This effect is known as dot gain, and it is considered as a typicalcharacteristic for the printing environment characterized for example bythe ink, paper and press combination. Therefore, if a spot color has tobe simulated, also for this spot color some dot gain has to be takeninto account to predict the exact color. Hence, a technique is requiredthat is able to predict the dot gain as if the colors were printed inoffset. To predict dot gain accurately, a number of parameters have tobe taken into account such as the types of ink and paper used. Inpractice dot gain can be predicted satisfactorily by specifying astandard dot gain curve. This curve represents the dot gain or dot lossas a function of the colorant values sent to the printing system.

A preferred embodiment of the invention is the following. An advantageof this embodiment is that it allows accurate reproduction of specificcolors, such as spot colors and custom colors. Moreover, the overlap ofsuch a specific color with another color, that may be a spot color, acustom color or a process color, may be output with high color quality.

A model for the color mixing between spot colors or between spot colorsand process colors is created based on an analysis of the image data,which include the spot color information. The model may be made thefirst time it is needed and applied “on the fly” pixel per pixel; or themodel may be made in advance before the image is processed and applied“on the fly” pixel per pixel; or the model may be made in advance,evaluated for a number of colorant combinations to obtain a colortransformation table, and the table is applied pixel per pixel by makinguse of interpolation techniques. The latter alternative is preferred,because it is computationally less intensive. In that case the completeimage may be analyzed to check the color characteristics. The analysisdetects the presence of non-process colors, as well as overlaps betweennon-process colors, and between process colors and non-process colors.The non-process colors (e.g. spot colors, custom colors) then receive aspecial treatment. A model encompassing these colors is made, asdiscussed below.

Spot Color Reproduction

The reproduction of a spot color can be considered as a model for a1-ink process. As printer model, it is preferred to use the Neugebauerequations, which are regarded as the basic model to predict colorreproduction, e.g. in offset printing. However, the Neugebauer modeldoes not predict dot gain. To simulate the dot gain behavior of aprinting process, the well-known Yule-Nielsen correction can be used.The disadvantage of this correction is that it is highly dependent onthe measurement technique, specifically the filters used for the colormeasurements and the model that is applied. Therefore, it is preferredto apply an improved dot gain correction that in general can bedescribed by a model that modifies the colorant value itself. Thismodified colorant value is then input to the Neugebauer model. Such animproved dot gain correction, i.e. improved with respect to theYule-Nielsen correction, may be obtained by making use of measuredvalues. These measurement values may originate from the measurement of aprinter target such as the IT8.7/3, IT8.7/4 or the ECI2002 target. Sucha target can contain either colorimetric data such as CIELAB and XYZ,densities or spectral information. For one of these data sets, curvefitting is applied to the measured values in ordinate, as a function ofthe colorant values in abscissa. In the simplest way, the data for the1-ink processes are taken from the measurement file and in betweenvalues are obtained by interpolation, e.g. linear interpolation. Fromthe obtained curve, the dot gain values for CMYK can be determined. Thiscan be calculated as the difference in dot percentage between the linearprocess between the 0% and 100% values and the fitted process. Forexample the dot gain for the 50% value has the following characteristic:the measurement value of the 50% value is equal to the measurement valueof the (50+dot gain) % value in the linear process. For spot colors, thesame dot gain behavior as for the process colors can be presumed. TheNeugebauer model is then applied to the dot gain corrected colorantvalues. Dot gain corrected values in our example can be obtained by thesum of the dot percentage and its dot gain.

For a 1-dimensional process, as is the case for the reproduction of asingle spot color, the Neugebauer model corresponds to linearinterpolation between the device independent color values of the paperand those of the 100% patch of the spot color. Preferably a tristimulusspace such as CIE XYZ is used for this interpolation; more preferably itis also used for the measurement values.

In a next step, the thus obtained device independent color values, e.g.in CIE XYZ, are transformed to the device dependent colorant values ofthe output system. If the output system is then addressed with thesedevice dependent colorant values, a reproduction of the image on theoutput system is made. The output system may be a proofing device, inwhich case a proof of the image is obtained. The transformation to thedevice dependent colorant values of the output system is a so-calledinverse transformation. If, for this inverse transformation, colortables are used, as within the ICC framework, sometimes the colors aredesaturated and a rendering intent may have to be used that is notnecessarily optimal for the rendering of spot colors. Therefore, anothermethod is sometimes preferred.

Analogously to the creation of the model for the output device discussedabove, the inversion may be created on the fly or in advance a dedicatedinversion table may be calculated. If processing speed is required, thelatter is preferred. If however, the transform has to be quite accurate,on the fly inversions are preferred in order to avoid interpolationerrors. To obtain a combination of both, a dedicated table with a smallstep can be built in advance, in order to allow accurate calculation ofthe transformation. If the colorant values for the output device arerepresented by 8 bit data, for the most accurate approach separationsfor all 256 colorant values are calculated in advance to be used totransform the spot color values in the device independent space to thecolorant space of the output system.

Reproduction of Two Spot Colors

In the case of two overlapping spot colors, only the calorimetric valuesfor the two individual 100% patches are given (such 100% patches arealso referred to as the solids). In this case too, a model is requiredto predict the calorimetric values of all possible combinations ofoverlap. However, in general not enough information is available to usea printer model. Let us take the Neugebauer model for a 2-ink process asan example. This model is given as follows:X=X _(p)(1c ₁)(1−c ₂)k ₀ +X ₁ c ₁(1−c ₂)+X ₂(1−c ₁)c ₂ +X ₁₂ c ₁ c ₂Y=Y _(p)(1−c ₁)(1−c ₂)k ₀ +Y ₁ c ₁(1−c ₂)+Y ₂(1−c ₁)c ₂ +Y ₁₂ c ₁ c ₂Z=Z _(p)(1−c ₁)(1−c ₂)k ₀ +Z ₁ c ₁(1−c ₂)+Z ₂(1−c ₁)c ₂ +Z ₁₂ c ₁ c ₂with (X_(p), Y_(p), Z_(p)) the XYZ values of the paper

-   -   (X₁, Y₁, Z₁) the XYZ values of the solid of the first spot color    -   (X₂, Y₂, Z₂) the XYZ values of the solid of the second spot        color    -   (X₁₂, Y₁₂, Z₁₂) the XYZ values of the overlap of both spot        colors    -   c₁ and c₂ the colorant value of the first and second spot color    -   (X, Y, Z) the XYZ values of the resulting color.

As can be seen from this formula, also the overlap of the two spotcolors is needed.

This issue may be solved by using the transmission spectra of the solidsand the reflectance curve of the paper to predict the calorimetricvalues of the 200% ink overlap. The simplest model that can be used arethe spectral Neugebauer equations. For even more accurate colorpredictions, corrections can be taken into account concerning severalphysical effects of light interactions at the ink surface, in the inklayers, between the ink layers and in the paper. Descriptions of thesephysical effects and corrections therefore can be taken from thespecialist literature.

Besides this spectral modeling, it is preferred also to incorporate dotgain effect. As discussed above, this effect may be modeled explicitly,e.g. by means of curves based on experimental data. Alternatively, dotgain values may be input by the user.

Similarly to the case of reproduction of a single spot color, theobtained colorimetric values (e.g. in CIE XYZ) are separated into thedevice dependent colorant values of the output device.

Reproduction of Process Colors and a Spot Color

Also in the case of mixing process colors and a spot color, a model isrequired that predicts the colors of all possible overlaps. This modelis preferably continuous with respect to the model that is used in theforward color separation tables for the process colors only. As thesetables are regular grids, the forward regular grid, for the four processcolors CMYK, can easily be extended with the spot color to obtain a5-dimensional ink process. All the combinations of process inks in theforward table are maintained, and the solid spot color value is given.However, to be able to use interpolation schemes within color tables, atleast all the corner points of the 5-dimensional colorant cube have tobe specified. Hence, all combinations of 0% and 100% for the processcolors and the 100% of the spot color have to be provided. To predictthese combinations, a printer model is needed. Also in this case, asimple spectral Neugebauer process with additional dot gain modulationcan be used. For even better prediction, more complex approachesmodeling different physical processes may be used. If a more accuratetable is required, additional combinations of spot color values inbetween 0% and 100% with colorant values of the process colors can bedetermined with the printer model, and filled out in the table. To keepthe 5-dimensional forward table as small as possible, preferably onlyexisting sampling points of the process colors are taken, with a minimumnumber of extra values for the spot color.

In this way a non-regular grid is obtained from which an irregularlocalized model can be constructed; for more details we refer to EP-A-1146 726, mentioned already above. Hence, a method is provided to build aforward model that is a trade-off between taking into account a minimumof extra patches and hence a model that is as small as possible, and amore accurate model by filling out more colorant combinations resultingin a larger forward table.

For the inverse transformation from the calorimetric space to thecolorant space of the output system, again, as discussed above, colortables may be used as within the ICC framework, or the inversion may becalculated on the fly, or a dedicated inverse separation table may becreated once, i.e. in advance.

If only a limited number of combinations (i.e. overlaps) of the spotcolor and the process colors are present in the image, e.g. the spotcolor is only printed with cyan and magenta but not with yellow andblack, then a smaller forward table can be constructed. In this way lesscolorant combinations have to be taken into account and a goodcontinuity is achieved between process colors on the one hand and thecombination of process colors and spot colors on the other hand.

If the image does not contain color gradations that are a combination ofa spot color and the process colors, then the number of combinations ofthe spot color and process colors is quite limited. In that case, onlyfor that limited number of combinations of process colors with the spotcolor, the resulting color has to be predicted, and the correspondingcolorant values of the output system may again be calculated in advanceor on the fly.

Reproduction of Process Colors and Several Spot Colors

The previous approach to predict the calorimetric values for the overlapbetween one spot color and process colors can easily be extended toseveral spot colors.

It is known in the art to create a model for an output device, and toinvert such a model, beforehand, i.e. before data on the image areavailable, which data include what colors and what overlapping colorsoccur in the image.

From the embodiments discussed above, it is clear that, in the presentinvention, a model may be created only when needed. Also the inversionon the fly may be used as needed. As computers get faster and faster,this option becomes more and more interesting.

In one embodiment of the invention, the image is to be output directlyon an output device. The output device may e.g. be an ink jet printer,or a printing device that uses printing plates, such as an offset press.The non-process colors may then be converted to the process colors ofthe corresponding output device; combinations of only process colors donot need to be transformed.

In another embodiment of the invention, the image is to be output on anoutput device such as an offset printing press, but first the image isto be simulated on a proofing device. In this case, first the printermodel of the offset press is applied to the image, and then the inversemodel of the proofer.

As mentioned already above, the model that is created preferably usesdata on the image; these image data may be determined by analyzing theimage, or data concerning the image may be input by the user. Take forexample an image that contains a particular spot color yellow, andsuppose that the color data, e.g. XYZ data, of this yellow result in adirty yellow being printed. The user can then override the color datafor this yellow.

In a particular embodiment of the invention, the data of the image thatis to be output are sent to the RIP, which stands for raster imageprocessor. Usually, the image data that are input to the RIP (e.g. inPostScript™ format) are already separated in data in process colors,usually CMYK, on the one hand and in separate data, per spot color used,on the other hand.

The following example illustrates a set of operations that may then beperformed in the RIP. First, a dot gain correction is applied. Then, amodel for the output device is created and applied to the spot colors.The spot color(s) are thus transformed to XYZ space. A rendering intent,that is specifically adapted to the spot colors, transforms the spotcolors to another XYZ space, say X′Y′Z′. Supposing that the image is tobe proofed on a proofing device, a gamut mapping for the proofer isapplied, followed by the inverse proofer model, which results incolorant values for the proofer. Possibly a smoothing step is applied.

In another embodiment of the invention, one or more of the precedingoperations are omitted.

For combinations, i.e. overlaps, of spot colors with other spot colorsor with process colors, it is preferred to use an accurate model as setout above. However, especially if overlaps between three or even morecolors occur, e.g. an overlap of a spot color with two process colors, asimplified “adding model” may also be used. For the color combinationsthat occur most, preferably an accurate model is applied. For the lessoccurring color combinations, the spot colors may be converted toprocess color space, which is usually CMYK, by means of interpolationbetween the colorimetric values of the receiving substrate and those ofthe 100% patch of the concerned spot color. The resulting CMYK values ofthe overlapping spot colors and process colors are then added. In case acolorant value of more than 100% is obtained, the colorant values arerescaled or, which is preferred, clipped.

The invention is not limited to embodiments described above. What wasdiscussed especially for spot colors, also holds for other non-processcolors, such as custom colors. The process colors may be CMYK, they maybe Hexachrome™ colors, they may be six colors including CMYK and twocolors selected from the group of orange, blue and green. Instead of aspectral Neugebauer model, another model may be used, such as polynomialfitting.

The invention includes a system and a method as disclosed above and asclaimed in the appending claims. The invention also includes a printingplate and a printing plate precursor made by a method in accordance withthe invention. A “printing plate precursor” is an imaging material thatcan be used as a printing plate after one or more treatment steps, thatinclude image-wise exposure and possibly processing: The inventionfurther includes a color proof obtained by a method in accordance withthe invention.

Having described in detail preferred embodiments of the currentinvention, it will now be apparent to those skilled in the art thatnumerous modifications can be made therein without departing from thescope of the invention as defined in the appending claims.

1. A method for reproducing an image including process colors in a firstcolorant space and a non-process color on a first printer having a firstprinter model, the first printer model being arranged to transform thefirst colorant space into a device independent color space, and thefirst printer model having an inverse first printer model arranged totransform the device independent color space into the first colorantspace, the method comprising the steps of: analyzing the image to detectfirst portions in the image having only process colors and secondportions having non-process colors; reproducing the first portions ofthe image in the first colorant space on the first printer; andreproducing the second portions of the image on the first printer by:creating a dedicated printer model that encompasses the non-processcolor and that has a one-to-one relation to the device independent colorspace; using the dedicated printer model to transform the secondportions into the device independent color space; using the inversefirst printer model to transform the second portions from the deviceindependent color space to the first colorant space; and reproducing thesecond portions in the first colorant space on the first printer.
 2. Themethod according to claim 1, wherein the first printer uses printingplates to reproduce the image.
 3. The method according to claim 2,further comprising the steps of: using the first printer model totransform the first portions from the first colorant space to the deviceindependent color space; using an inverse second printer model toconvert the first and second portions from the device independent colorspace to a second colorant space of a second printer; and reproducingthe first and second portions in the second colorant space on the secondprinter.